As functions of electronic products become more and more complicated while electronic products are becoming smaller and portable, especially with extensive use of wireless communication terminals, higher requirements are put forward for designers, for example, lower power consumption, small amount of the whole dissipated heat, and higher reliability are required. Actually, smaller products will badly impede heat dissipation, which results in poor heat dissipation to reduce the reliability of the products. Therefore, the whole power of an electronic product can be reduced to effectively reduce the whole dissipated heat, and increase the reliability.
Generally, a portable wireless terminal product is provided with a charging function. Therefore, it is of great significance to study linear charging circuits in increasing the charging efficiency. Currently, to solve the problem above, a first existing technique discloses the following technical solution: a dynamic feedback control circuit is added in a charger to increase the transient load variation by regulating the output voltage, so that the output voltage of the charger is close to the voltage of the battery and the power consumption is reduced. A second existing technique discloses the following technical solution: a TL494 (pulse-width modulation control circuit) pulse-width modulation component which controls the output voltage and current is applied, and improved constant-current charging is utilized; in the initial stage, the current is large and the voltage is low, and then the current is reduced gradually and the voltage is increased gradually to avoid over-charging. It can be seen from the first and second existing techniques that both solutions increase the charging efficiency by regulating the charging voltage and the charging current of the charger.
Currently, since Universal Serial Bus (USB) interfaces, which have excellent data transmission capability and capability of power supply for the peripheral equipment, are convenient to use and applied broadly, the USB interfaces are used as charging interfaces by more and more electronic products with charging function, so that data interfaces and charging interfaces are unified. Linear charging circuits are used by all portable wireless communication terminals, such as mobile phones etc, which can be generally charged by adapters or USB interfaces of PCs. If a high-efficiency charging device is mounted on an electronic product, the charging efficiency will be increased no matter the electronic product is charged by an adapter or a USB interface of a PC. The voltage is low at low battery power, and the voltage of the battery will be increased with the increase of the battery power. During the charging process, there is a changing voltage difference between the input voltage and the voltage of the battery, which mainly acts on a charging tube, thus causing unnecessary energy loss which is more serious especially when the charging current is relatively large.